1. Field of the Invention
The present invention relates to a method and an equipment for treating microcystin-containing water, more particularly to a method and an equipment for treating microcystin-containing water that can degrade and detoxify microcystin produced from algae such as water-bloom generated in closed-water areas such as lakes, dams, moats, and inland seas.
2. Description of the Related Art
When closed-water areas such as lakes, dams, moats, and inland seas are eutrophicated due to inflow of sewage or the like, a large amount of cyanobacteria, for example, cyanobacteria belonging to the genus Microcystis are proliferated in the closed-water areas to generate so-called water-bloom. Many types of the cyanobacteria including the generated water-bloom produce microcystin called water-bloom toxin, and thus the closed-water areas are polluted with microcystin. Microcystin is composed of a cyclic peptide consisting of seven amino acids, and has properties of toxic and carcinogenic to a liver of human or livestock.
Microcystin LR, microcystin RR, and microcystin YR detected as typical microcystins from closed-water areas make human or livestock poisoned when the microcystins are orally ingested. There are various reports on poisoning by the microcystins in Japan and other countries, irrespective of human or livestock (see Mariyo WATANABE, “Water-bloom”, University of Tokyo Press, 1999, and Kenichi HARADA, “Recent Advances of Toxic Cyanobacteria Researches”, Journal of Health Science, 45(3), 150-165, 1999). However, since the mechanism of liver diseases due to the microcystins has not been clear, there is no method for treating the poisoning actually.
Conventionally, various methods for treating microcystin have been studied. In order to prevent poisoning by microcystin, a method for suppressing the generation of water-bloom is generally used.
As the method for suppressing the generation of water-bloom, a method is adopted to add an algae proliferation inhibitor such as lysine to a closed-water area with generated water-bloom. In addition, a method is also adopted to spray an algaecidal copper ion compound over a closed-water area with generated water-bloom, as described in Japanese Patent Application Publication No. 9-239370.
In Japanese Patent Application Publication No. 8-33888, a method is also suggested to transmit ultrasonic waves to polluted water prepared by evacuating a part of a closed-water area with water-bloom generated, thereby crushing cells of water-bloom so as to destroy the algae.
However, the produced microcystin is accumulated in the cells of the cyanobacteria. Even if the water-bloom is removed by the above-described methods, a large amount of microcystin is released from the crushed cyanobacteria. Therefore, there is a problem that the closed-water area is increasingly polluted with microcystin.
In order to resolve this problem, Japanese Patent Application Publication No. 11-70395 discloses a method of oxidation degradation with ozone, and a method of oxidation with chlorine, as a method for treating microcystin produced from water-bloom.
However, in the method of adding an algae proliferation inhibitor, since the algae proliferation inhibitor itself is an organic substance such as lysine, then BOD concentration in a closed-water area is increased by the addition of the algae proliferation inhibitor, which causes organic substance pollution.
In the method described in Japanese Patent Application Publication No. 9-239370, since a large amount of copper ion compounds remains in water in a closed-water area, it is not preferable that the water is used to be drunk.
The method described in Japanese Patent Application Publication No. 8-33888 has drawbacks in that oscillation of ultrasonic waves requires a massive amount of energy, and the residual crushed cells cause secondary pollution such as eutrophication.
In the method described in Japanese Patent Application Publication No. 11-70395, and the method of oxidation with chlorine, it is possible to completely degrade microcystin itself in a closed-water area. However, in such methods, since ozone or chlorine is reacted with a large amount of contaminants in a closed-water area, there is problem in that microcystin cannot be degraded efficiently. In addition, there is also a problem that a toxic by-product such as trihalomethane is generated due to the strong oxidation ability of ozone or chlorine.